1. Field of the Invention
This invention relates to a linear motion rolling guide unit providing guide operation by rolling rollers on raceway faces formed in a track rail, and provided with underside seals for preventing the intrusion of dust to the raceway faces.
2. Description of the Related Art
One of the conventional linear motion rolling units of the type described above is disclosed in Jp. Patent Publication No. 3237981 as illustrated in FIGS. 8 to 10, for example. The conventional guide unit includes two raceway faces 1 and 2 formed on each side face of a track rail R, and a slider S straddling and running on the track rail R having the raceway faces 1 and 2.
The slider S is provided with end caps 3 and 4 respectively combined with the front and back ends of a casing c. The slider S is bilaterally symmetrical with respect to the axis of the track rail R. Therefore, the structural elements having the same shape in bilateral symmetry will be hereinafter described by use of the same reference numerals or symbols.
A pair of guide holes 5 and 6 is formed in the casing c. The guide holes 5 and 6 extend through the casing c in the axis direction parallel to each other in upper and lower positions. Guide cylinders 7 and 8 are respectively inserted into the guide holes 5 and 6.
Each of the guide cylinders 7 and 8 is made up by combining two semicircular cylinder members together. Circular-cylindrical rollers 9 and 10 are incorporated in the guide cylinders 7 and 8 in such a manner as to allow them to roll therein. The circular-cylindrical rollers 9, after rolling in the upper guide cylinder 7, are guided in a direction that brings them into contact with the lower raceway face 2, while the circular-cylindrical rollers 10, after rolling in the lower guide cylinder 8, are guided in a direction that brings them into contact with the upper raceway face 1. The circular-cylindrical rollers 9 and 10 guided in this manner run inside the end cap 3 or 4 while crossing each other without interfering with each other.
Underside seals 11 and 12, each including a cored bar around which a rubber material is wrapped, are secured on the underside of the slider R. Each of the underside seals 11 and 12 has a longer length than the entire length of the casing c so that the two ends of the, underside seal respectively face the end caps 3 and 4 which are provided at the respective ends of the casing c. Long holes 13 and 14 are drilled in portions of the ends of each of the underside seals 11 and 12 in the longitudinal direction thereof.
A pair of hooks 15a, 15b and a pair of hooks 16a, 16b are formed on the respective undersides of the end caps 3 and 4 of the slider S, and fitted into the long holes 13 and 14.
FIG. 10 illustrates the underside seal 11 (12) hooked as described above. As seen from FIG. 10, each of the underside seals 11 and 12 is secured to the casing c with a bolt 17. The leading end (in the sectional view of FIG. 10) of each of the secured underside seals 11 and 12 seals a side face 18 of the track rail R to prevent the intrusion of dust into the area including the lower raceway face 2 and the circular-cylindrical rollers rolling on the lower raceway face 2.
FIGS. 8 and 9 show end seals 19 and 20 and bolts 21 and 22 for securing the end seals 19 and 20 to the end caps 3 and 4. The end seals 19 and 20 have projections 19a and 20a formed on their inner sides. The projections are fitted into the recessed grooves formed between the raceway faces 1 and 2 of the track rail R and can slide thereon.
These days, what is required is a very small-sized guide unit with a track rail about 10 mm wide having raceway faces, but the foregoing conventional guide unit cannot answer this requirement of a reduction in size due to the following reasons.
The reduction in size of the entire guide unit reduces the size of the slider S and end caps 3 and 4 as a natural consequence. However, in the conventional guide unit, the hooks 15a, 15b, 16a and 16b are formed on the end caps 3 and 4. The more the size of the end cap is reduced, the more difficult the formation of the hooks 15a, 15b, 16a and 16b on the end caps 3 and 4 becomes. A first reason for the impossibility of the ultra-reduction in size is that the ultra-reduction in size of the end caps results in the difficulty of forming the hooks 15a, 15b, 16a and 16b. 
Even if the hooks 15a, 15b, 16a and 16b can be formed on the end caps 3 and 4, it is difficult to maintain the strength of the hooks. Accordingly, a second reason for the impossibility of the ultra-reduction in size is that the reduction in size of the end caps results in the impossibility of maintaining the strength of the hooks 15a, 15b, 16a and 16b. 
Further, the bolts 17 are required to secure the underside seals 11 and 12, because the long holes 13 and 14 and the hooks 15a, 15b, 16a and 16b are by themselves insufficient to provide the force for holding the underside seals to the slider S. However, if the size of the guide unit is reduced, thin and narrow underside seals 11 and 12 must be necessary. To secure the thin and narrow underside seals 11 and 12 with the bolts 17 involves a high degree of difficulty and effort from a workability viewpoint. Accordingly, a third reason for the impossibility of the ultra-reduction in size is the impaired workability for securing the underside seals 11 and 12 with the bolts.